This invention relates generally to methods and apparatuses for communicating broadband signals between multiple customers and, more particularly, to methods and apparatuses for communicating using a low-cost, easily maintainable, fast deployable communication system capable of broadband and network communication in various environments.
Wireless data and telephony communication systems are quickly replacing conventional communication systems. Conventional terrestrial wireless telephony relies on unobstructed Line-Of-Sight (LOS) paths or close range multi-paths between the sending and receiving stations. This technology is easy to maintain. However, the communication range of operation is limited. The LOS restriction is particularly important for special mobile units, such as off-road vehicles. The local terrain quite often dictates vehicle position relative to the sending and receiving units in order for unobstructed communication to occur. Also, land-based wireless infrastructures are expensive to deploy and maintain, especially in remote areas.
FIG. 1 depicts a schematic diagram of a portion of a typical wireless telecommunications system designated generally as 10. System 10 serves a number of wireless terminals 22 and 24 that are situated within a geographic area. System 10 comprises wireless switching center 12 that is connected to a number of base stations 14, and that is also coupled to local and long distance telephone networks 16. Wireless switching center 12 is responsible for, among other things, routing or “switching” calls from and to wireless terminals or, alternatively, between a wireless terminal and a wireline terminal connected to wireless system 10, via local and/or long distance telephone networks 16.
The geographic area serviced by wireless system 10 is partitioned into a number of spatially distinct areas called cells. As depicted in FIG. 1, each cell 20i is schematically represented by a hexagon. In practice, however, each cell 20i usually has an irregular shape that depends, for example, on the topography of the terrain serviced by system 10. Typically, each cell 20i contains a corresponding base station 14i. Base station 14i comprises antennas and radios to communicate with wireless terminals 22 and 24. Each base station 14i also comprises transmission equipment to communicate with wireless switching center 12.
In designing system 10, engineers allocate a limited number of frequency channels to each base station 14i using well known techniques. Base stations 14i communicate with wireless terminals over these frequency channels. Thus, the number of base stations limits the potential capacity of system 10 for processing calls to and from wireless terminals.
Present wireless communication systems fail to provide broadband wireless communication in real time across extended distances while maintaining a LOS path between stations where one or both stations may be in motion. Many regions of the world today have a sparse or no fixed communication infrastructure and lack the resources needed to upgrade their existing equipment to match more developed areas. Wireless communication systems are an effective tool for providing this service. However, present wireless systems fail to meet the needs of specific applications.
A factor impacting traditional wireless communication infrastructures is the huge increase in demand for communicating broadband services consisting of voice, video, and data information. Because of inherent limitations in the transmission media, wireless communication must compensate for noise introduced in the radio path. The following are wireless techniques for compensating for noise: 1) restricting the range; 2) increasing the transmitted signal amplification or power; 3) increasing the received signal amplification; 4) increasing the error correcting efficiency; 5) changing the radio signal modulation or frequency to reduce the impact of noise; or 6) a combination of any or all of these techniques. However, all of these techniques affect the cost and complexity of a wireless system. Moreover, compensating for unreliable wireless paths becomes increasingly difficult as the data rate increases.
Various satellite-based solutions have been proposed to address the above identified issues, but are generally too costly unless applied over continental or larger geographic areas. Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) based systems aspiring to global coverage do so at the expense of operating satellites over the two thirds of the earth covered by water. Additionally, the often huge increase in wireless earth-space-earth path distance between terrestrial stations adversely impacts satellite-based solutions because of the end-to-end transmission delay and increased path loss. Thus, real-time communication is impractical at higher orbital altitudes. This is especially the case with Geosynchronous Earth Orbit (GEO) satellite systems. An optimally-designed three-stage chemical rocket typically must be 94% propellant at launch to reach geosynchronous orbit, which, after allocating about 5.6% of the weight for the rocket, only leaves about 0.4% of the initial launch weight for the satellite. To put this in perspective, a typical 3,000 lb. automobile with the same performance would only be able to carry one 200 lb. person, would need a 8,400 gallon fuel tank, and would be junked after one trip.
The following are other drawbacks or implementation difficulties of GEO satellites: 1) the high cost of launching the satellites into the geostationary orbit; 2) long inter-satellite link distances; and 3) high transmit power requirement. Neither satellite-based or fixed land-based systems easily facilitate transient demands for communication in remote areas. Presently, no communication infrastructure exist for allowing economic operation within a relatively confined geographical area for service that may have fluctuating demand and require rapid deployment of the system.
FIG. 2 shows a known communication system in which the platform supporting base station 314 is a high altitude balloon 326. The high altitude balloon 326 is capable of maintaining altitudes greater than 120,000 feet above sea level for periods of time exceeding several months while supporting a payload.
High altitude balloon 326 is provided with a streamlined body to facilitate horizontal movement while minimizing the effect of winds on balloon 326. Balloon 326 includes propulsion system 332 which may be in the form of propeller 334 driven by an electric motor. A power supply, such as solar cell array 336, is positioned on the balloon envelope to supply energy during daytime to drive propulsion system 332 and to charge batteries 338. Batteries 338 supply energy to propulsion system 332 during nighttime flight. Although balloon 326 is disclosed as having propulsion system 332 including propeller 334 driven by an electric motor, an appropriate propulsion system capable of maintaining balloon 326 in a substantially stationary position over the earth may be used, e.g., jet engine, rocket engine, ion engine, etc.
As shown in FIG. 2, an RF signal transmitted by wireless terminal 322 is received by base station 314 defining the cell from which the RF signal was transmitted. The RF signal is converted from microwave at base station 314 using demodulation techniques and base station 314 communicates via microwave link 340 with wireless switching center 312. The RF signal is converted to microwave via block conversion which allows a single wireless switching center 312 to handle all of the processing for hundreds of base stations. If the signal is directed to another wireless terminal, wireless switching center 312 returns the signal along with routing data to base station 314 via microwave link 340. Thereafter, the signal is routed, according to the routing data, to the appropriate wireless terminal. If the signal is directed to a wireline terminal, wireless switching center 312 will route the call to the appropriate wireline terminal.
Unfortunately, the high altitude balloon 326 is currently very expensive to build and operate and such balloons do not yet have operating experience which proves that they can be reliable enough for economically attractive use.
There are two key challenges for providing a widely attractive airborne basestation that have not previously been overcome in previous systems. The two key challenges are cost and weight for the communications equipment. Prior systems have been both cost prohibitive and so heavy as to keep all inexpensive lighter-than-air vehicles gravitationally pinned to the ground.
Accordingly, there is a need in the art for a low-cost, easily maintainable, fast deployable communication system capable of broadband and network communication in various environments. Embodiments of the present invention are directed at providing such a communication system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.